Turning 17-4 (A)

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Matt in TN
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Turning 17-4 (A)

Post by Matt in TN » Tue Jun 25, 2019 12:08 pm

After all I've read about the difficulties machining 17-4 (especially in it's "annealed" state, which seems to be the cheapest/easiest way to buy it), I was hesitant to try it on my 1955 Southbend 9A. I'm pretty much limited to HSS tooling by the lathe speed limitations, and my only lubrication setup is with a squirt bottle and brush.

But for my 30 cal design I found I could cut my thicknesses in half with 17-4 vs 416 (what I used on my 22LR suppressor), and should see better wear resistance as well - so I tried it. This post is for all those who are stuck in my boat and afraid of it - it wasn't that bad!

My little lathe can't spin fast enough to cut what I found the recommended SFM was (300-400 SFM depending on operation), and when I tried to take the recommended depth of cut and feed rate my lathe bogged down and stopped. So I found as happy a medium as I could - reducing the RPM to get more gear advantage and avoid the bog down, reduce the depth of cut a little, and feed by hand as heavy as the lathe could handle. Also - by doing everything by hand I could better react and change directions quickly, as the other thing I read about 17-4 is that it work hardens easily. If you're not feeding in, you want to jump right out right away - do NOT let the tool sit still and rub or it will work harden right away. Also keep the tooling SHARP so you cut instead of rub/burn. And then sand out any tool marks left by all the hand feeding.

After playing with several different HSS tooling grinds and trying different feeds and speeds I think I've got it. My blast baffle was thickest (0.100" wall), so I started with it. Now that I have the process down I'm moving on to the other baffles which will be half as thick (0.050" wall). I should add - the tubing and spacers in the pic are titanium from Diversified Machine, and I did not cut those.

Image

Anybody else cut this stuff on smaller machines? What works for you?

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Re: Turning 17-4 (A)

Post by ECCO Machine » Tue Jun 25, 2019 2:42 pm

17-4 is a really easy stainless grade to work with, gives better surface finishes than just about any other annealed steel as long as you keep temperatures reasonable. The tough, stringy chips are annoying and a bit hazardous, but as long as you're conscious of that, it's a very pleasant metal to work with.
Matt in TN wrote:
Tue Jun 25, 2019 12:08 pm
I'm pretty much limited to HSS tooling by the lathe speed limitations
Que?

You can't run the higher speeds with HSS, but you can absolutely go slower with carbide. The only time you really have to worry about carbide & low speeds is interrupted cuts.

S&F charts are a good baseline until you gain familiarity with your machine, your tooling and the materials, but as time goes on, you're gonna find yourself outside of those recommended numbers more often than not on manual equipment. Your machine will tell you what speeds and cut depths it likes with any given tooling on a particular material. Well, it's more that it'll tell you what it doesn't like, but you get my point.
Last edited by ECCO Machine on Tue Jun 25, 2019 2:45 pm, edited 2 times in total.
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Re: Turning 17-4 (A)

Post by ECCO Machine » Tue Jun 25, 2019 2:43 pm

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Re: Turning 17-4 (A)

Post by fishman » Tue Jun 25, 2019 3:26 pm

I cut it with a tiny lathe. See links below.
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

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Re: Turning 17-4 (A)

Post by T-Rex » Tue Jun 25, 2019 3:38 pm

My SB 9A is from, IIRC, 1947. I was able to use carbide tooling and take quite generous cuts. It's a nice metal to work with, especially for being stainless.
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Re: Turning 17-4 (A)

Post by Matt in TN » Tue Jun 25, 2019 4:39 pm

T-Rex wrote:
Tue Jun 25, 2019 3:38 pm
My SB 9A is from, IIRC, 1947. I was able to use carbide tooling and take quite generous cuts. It's a nice metal to work with, especially for being stainless.
Interesting. I tried carbide early in my "career" and it didn't go well. I read somewhere it needed really high speeds, so I gave up on it. Maybe I should revisit that idea thanks to you and ECCO. Any tips where to start? Inserts, brazed on, etc?

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Re: Turning 17-4 (A)

Post by Matt in TN » Tue Jun 25, 2019 4:41 pm

I should have mentioned the chips - thanks ECCO. I struggle with steel spaghetti pretty regularly and haven't done very well with chip breakers. So I come up with fairly safe ways to handle the sharp spaghetti and just deal with it. It's definitely something to be aware of, though.

Maybe one day my chip breaking abilities will improve...

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Re: Turning 17-4 (A)

Post by ECCO Machine » Tue Jun 25, 2019 6:24 pm

Matt in TN wrote:
Tue Jun 25, 2019 4:39 pm
Any tips where to start? Inserts, brazed on, etc?
For most purposes, I use inserts, the holders in turn mounted to QCTP tool holders. Inserts are cheap, and if you dull or break one and have to change it out, you don't need to re-zero unless you're trying to hold <.002" tolerances.

It is handy to have some cemented carbide tools around for grinding profiles, though. You're pretty limited on shaping inserts due to the support of the holders.

There are tons of insert types, and while I don't have time right now to get into everything I know about them right now, I can tell you that I do 90% of my turning with CNMG, TNMG, CCMT and MGMN.

The most important thing running carbide, whether on a lathe or mill, is rigidity; they'll chip or break much easier than HSS from chattering, suddenly getting too big a bite, or anything else that shock loads the tool. Wiggly/sloppy machines and carbide don't play well together.
Matt in TN wrote:
Tue Jun 25, 2019 4:41 pm
I should have mentioned the chips - thanks ECCO. I struggle with steel spaghetti pretty regularly and haven't done very well with chip breakers. So I come up with fairly safe ways to handle the sharp spaghetti and just deal with it. It's definitely something to be aware of, though.

Maybe one day my chip breaking abilities will improve...
A lot of the carbide inserts have good chip breaking designs, but even with those, about the only way to avoid stringing with 17-4 in any condition is really aggressive feed rates with decent DOC, probably more than your SB can handle. I can get good chip breaking on my Rahn-Larmon, but that's a 4,000 lb 17x60 machine.
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Re: Turning 17-4 (A)

Post by T-Rex » Tue Jun 25, 2019 7:24 pm

I got the best chips from interior profiling and an, IIRC, SCLR insert. For the exterior, I do believe I have CNMG. My insert game isn't very strong, but I've found what seems to work and what doesn't. I have a good selection of inserts and bars, but have yet to spend a dime. I received a good deal when a friend passed and the rest from an acquaintance, who bought a ton of machinist stuff at auction. He didn't need any of the smaller items and handed them off to me. If I had to buy any of it, I would have a lot of reading to do. Instead, I gave it a try and either ruined an insert or found my new best friend.

For simple boring or interior profiling, I prefer the carbide. I'll go to HSS for grooving or interiors that "open-up". However, the reverse seems to be true for the exterior. Simple turning is great w/ HSS and I usually use carbide for special cuts or those pieces of metal that prefer it. Exterior threading is almost always done w/ carbide. I don't mind doing it at a higher rpm. Interior threads depend on my ID. If I can manage to get the insert bar in there, I will.
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Re: Turning 17-4 (A)

Post by cdhknives » Thu Jun 27, 2019 6:19 pm

My Atlas 10F is from the mid 1940's and runs carbide inserts just fine...once I got the play out of the toolholder. Your 9A will do it too. My big issue to overcome was a wobbly lantern style toolholder. That lead to chipping inserts right quick! Once I got a good solid QCTP I have no problem with carbide inserts running the moderate speed+feed this light lathe can achieve.

I use 17-4 for my mounts and blast baffle, for thread strength and wear resistance. Al or Ti for the rest. Carbide cuts them all. Yes the stringy chips will cut you!
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Re: Turning 17-4 (A)

Post by Matt in TN » Sat Jun 29, 2019 12:09 am

You guys talked me into it. I just ordered this kit to try carbide again and see if I do better this time: [url][https://latheinserts.com/1-2-HOBBY-LATH ... it.htm/url]

To be fair, the last time I tried it I had JUST started with the lathe, so the issue very well could have been operator-induced.

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Re: Turning 17-4 (A)

Post by Paco664 » Mon Jul 01, 2019 2:43 pm

Matt in TN wrote:
Sat Jun 29, 2019 12:09 am
You guys talked me into it. I just ordered this kit to try carbide again and see if I do better this time: [url][https://latheinserts.com/1-2-HOBBY-LATH ... it.htm/url]

To be fair, the last time I tried it I had JUST started with the lathe, so the issue very well could have been operator-induced.
to be fair 99.99% of my mistakes on the lathe are operator induced.... lol...

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Re: Turning 17-4 (A)

Post by mr fixit » Mon Jul 01, 2019 9:40 pm

This is what I bought:
https://www.amazon.com/OMEX-INDEXABLE-H ... -1&sr=8-9

I use them with a 12" Logan. All of the tools use the same insert type, either CCMT for most steels and stainless, and CCGT for Aluminium but which cuts Titanium like butter.

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Re: Turning 17-4 (A)

Post by Matt in TN » Tue Jul 02, 2019 6:56 am

mr fixit wrote:
Mon Jul 01, 2019 9:40 pm
This is what I bought:
https://www.amazon.com/OMEX-INDEXABLE-H ... -1&sr=8-9

I use them with a 12" Logan. All of the tools use the same insert type, either CCMT for most steels and stainless, and CCGT for Aluminium but which cuts Titanium like butter.
Dang - where were you last week? That looks like a much better deal than what I bought!

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Re: Turning 17-4 (A)

Post by Matt in TN » Tue Jul 16, 2019 10:37 pm

Matt in TN wrote:
Sat Jun 29, 2019 12:09 am
You guys talked me into it. I just ordered this kit to try carbide again and see if I do better this time: [url][https://latheinserts.com/1-2-HOBBY-LATH ... it.htm/url]

To be fair, the last time I tried it I had JUST started with the lathe, so the issue very well could have been operator-induced.
This came in, and it cuts like butter. Not sure if it was my skills or the tooling that was lacking last time I tried this. I just ordered several more tool holders so I could do more with this. Thanks for the push!

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Re: Turning 17-4 (A)

Post by Capt. Link. » Thu Jul 18, 2019 9:52 pm

You might try insert HSS tooling from AR Warner.The T-15 HSS cobalt tools will breeze through 17-4 and can be resharpened.While carbide is great for production work the cost can be very high for amateur work.Interrupted cuts and vibration are common with smaller machine tools and this kills a carbide edge.I have heard many people say they use carbide tooling on a small lathe but few ever mention how many carbide inserts they used for a given job.
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Re: Turning 17-4 (A)

Post by #40Fan » Fri Jul 19, 2019 1:56 am

The insert that I have broke the most has been for my parting tool. That was in the beginning when I didn't know better. I have dulled a few others and broke a couple more when the tool fell off of the bench. But, I do buy the cheapest inserts I can get from China.

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Re: Turning 17-4 (A)

Post by ECCO Machine » Sat Jul 20, 2019 11:45 am

Capt. Link. wrote:
Thu Jul 18, 2019 9:52 pm
You might try insert HSS tooling from AR Warner.The T-15 HSS cobalt tools will breeze through 17-4 and can be resharpened.While carbide is great for production work the cost can be very high for amateur work.Interrupted cuts and vibration are common with smaller machine tools and this kills a carbide edge.I have heard many people say they use carbide tooling on a small lathe but few ever mention how many carbide inserts they used for a given job.
It's definitely a trade off. I'm not using a small machine, and I still go through a lot of CCMT and MGMN inserts not having coolant flooding and cutting aggressively, but time is money, and I'd rather rotate or replace cheap inserts and not have to re-zero than spend 5 minutes resharpening HSS or cobalt and have to find zero again. With standard tolerance parts and a good DRO, you'll never have to find zero again running inserts as long as your tool post/holders are solid.

You don't have to break the bank on inserts, either. These are the CCMT I use:

https://www.ebay.com/itm/100pcs-CCMT060 ... SwSPBaVH0o

They're labeled as "Mitsubishi.......Made in Japan", which is obviously no more true than the $50 RMRs you can buy. But they work just fine, and I can typically cut 3 or 4 normal sized 17.4 baffles before they need rotated, another 3 or 4 before insert replacement. On 7075 or 7068 aluminum, more than double that. Ti is harder on them, each baffle pretty well smokes an edge, so I get a fresh cutting edge for the final pass on each baffle, then run that edge until it's time for the next final pass.

I could make my inserts last a lot longer if I didn't mind taking much shallower cuts at lower feed rates, but again, time is money, so saving a few inserts isn't worth doubling or tripling my manufacturing time.

One thing I forgot to mention earlier in this thread, but if you do want to go after 17-4 pretty hard, spraying your part with both gear oil and water works very well, keeps your tool cooler and minimizes the smoke. I'll make a video some time.
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Re: Turning 17-4 (A)

Post by 3strucking » Mon Jul 22, 2019 6:13 am

I use both HSS inserts from AR Warner and carbide inserts. I like both.

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Re: Turning 17-4 (A)

Post by Matt in TN » Mon Jul 22, 2019 10:08 pm

ECCO Machine wrote:
Tue Jun 25, 2019 6:24 pm

There are tons of insert types, and while I don't have time right now to get into everything I know about them right now, I can tell you that I do 90% of my turning with CNMG, TNMG, CCMT and MGMN.
Now that I'm learning more I'd like to revisit this. Why do you and T-Rex prefer CNMG? I would think the 0° rake would not cut as well as the 7° rake on the CCMT. Or is it simply that it cuts well enough, but with the 0° rake you effectively get twice as many cutting edges so your insert lasts twice as long?

And what does the MGMN do that the others don't? I don't understand that one -

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Re: Turning 17-4 (A)

Post by ECCO Machine » Tue Jul 23, 2019 12:29 pm

Matt in TN wrote:
Mon Jul 22, 2019 10:08 pm
Now that I'm learning more I'd like to revisit this. Why do you and T-Rex prefer CNMG? I would think the 0° rake would not cut as well as the 7° rake on the CCMT. Or is it simply that it cuts well enough, but with the 0° rake you effectively get twice as many cutting edges so your insert lasts twice as long?

And what does the MGMN do that the others don't? I don't understand that one -
The holders give the rake, just like TNMG and others.

CNMG inserts are thick; you can be really aggressive.

MGMN are parting/grooving inserts, but they work very well for cutting the outside profile of baffle cones with minimal material waste. I use MGMN300 insert MGEHR2020 holders for this, except aluminum rimfire baffles, which I do with MGMN200.
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Re: Turning 17-4 (A)

Post by Matt in TN » Mon Sep 16, 2019 5:36 pm

I got distracted with another project, but am back on this now. Happy to report the carbide inserts work great with my little Southbend 9A. Not sure if my problem before was cheap chinese tooling or a lack of rigidity, but it works great now. Still getting long stringy swarf, but I know how to deal with that.

Back to making baffles! Only 6 more to go...

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Re: Turning 17-4 (A)

Post by ECCO Machine » Tue Sep 17, 2019 9:17 am

Matt in TN wrote:
Mon Sep 16, 2019 5:36 pm
Still getting long stringy swarf, but I know how to deal with that.
That's pretty much unavoidable unless you keep up very aggressive feed rates. I've tried all kinds of different inserts with different chip breaking patterns, little difference. 17-4 is just tough stuff.

I usually grab the strings with pliers. The other day a really fine string was half in the can. I went to grab the part hanging out and stuff it in, didn't realize I was standing on the other end. Yeah.....that was a razor blade string.
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Re: Turning 17-4 (A)

Post by Matt in TN » Thu Sep 19, 2019 9:50 pm

ECCO Machine wrote:
Tue Sep 17, 2019 9:17 am
Yeah.....that was a razor blade string.
I bet! I did get it to chip better with really heavy feedrates, but my little lathe just couldn't handle it. I also set up for what I thought was a final cut, but ended up cutting much deeper than I intended and the part started turning straw yellow immediately from the heat. But the insert kept cutting, so I figured I'd just keep going and see what happened. I tried to add some oil to cool it off, but my brush bristles meted immediately (the black streaks).

The pic doesn't do it justice - it was a beautiful golden straw color with black streaks and bright magenta swarf! And the dang thing kept cutting just fine. Those inserts sure do put up with more abuse than my HSS tooling.

Image

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Re: Turning 17-4 (A)

Post by ECCO Machine » Thu Sep 19, 2019 9:56 pm

Matt in TN wrote:
Thu Sep 19, 2019 9:50 pm


The pic doesn't do it justice - it was a beautiful golden straw color with black streaks and bright magenta swarf! And the dang thing kept cutting just fine. Those inserts sure do put up with more abuse than my HSS tooling.
They will, but it embrittles them and they start to chip or fracture. High heat will also cause the material to gall & stick to itself.

Try keeping a high pressure oiler full of gear oil and a squirt bottle full of tap water on hand. A shot of the oil and then being liberal with the water will help keep finishes nice and prolong tool life, especially when boring. It's a little messy, but the water will mostly evaporate, and it's not like gear oil everywhere is bad for the machine.
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